Spent nuclear fuel generates radiation and heat for a long time due to a nuclear fission product included therein even after being pulled out from a nuclear reactor. Accordingly, in order to protect workers who work in an electric power station from radiation and to remove continuously generated heat, the spent nuclear fuel is stored in a water tank installed in a fuel building of the electric power station. A reinforced concrete structure in which the spent nuclear fuel is stored is called a spent fuel storage pool.
The spent nuclear fuel burned in a nuclear power plant has been wet-stored in the spent nuclear fuel storage pool which is an on-site storage facility. However, when the spent nuclear fuel storage pool reaches saturation point, the spent nuclear fuel, which has been burned, should be conveyed to and then stored in an intermediate storage facility. In the case where the spent nuclear fuel is intended to be conveyed to the facility for intermediate storage of the spent nuclear fuel, according to “the announcement of regulations for the delivery of spent nuclear fuel”, an operator of the intermediate storage facility of the spent nuclear fuel should inspect all the matters concerning the burnup of a spent nuclear fuel assembly and the like and should then take delivery of the spent nuclear fuel. Thus, an inspection technique therefor has been needed.
Despite the fact that many measurement apparatuses for identifying burnup using gamma rays, neutrons generated from the spent nuclear fuel assembly, or a combination of them have been developed, it is disadvantageous in that the measurement apparatuses have too complicated configurations to apply to inspection and have a limit of measurement environment.
In order to measure the burnup of a spent nuclear fuel assembly, gamma rays coming from the spent nuclear fuel assembly should be first measured using a sensing part, and the burnup of the spent nuclear fuel assembly is then measured based on intensity of the measured gamma rays.
Although detectors measuring gamma rays using a scintillator have been recently developed, a technique for using such a scintillator is environmentally restricted because the scintillator should be maintained at an extremely low temperature in order to increase efficiency of a sensing part which reacts to gamma rays.
Even though there is also a case in which an optical fiber is used in order to sense gamma rays, it is problematic in that the technique has, as a technique for measuring gamma rays using a sensing part having an optical fiber scintillator (OFS), a limit in performing accurate measurement due to an extinction effect that is a problem generated from a scintillator.